1. Field of the Invention
The present invention relates to apparatus for automatically retrieving desired data or information on an information bearing medium such as recording film or tape by detecting marks on the medium and counting the detected marks.
2. Description of Prior Art
In the art it is known to retrieve desired image data or information previously recorded on a film by counting particular marks provided on the side of the individual images in the film. When the number of the counted marks coincides with the address of the desired image, the film-feeding device is stopped. This conventional retrieving method involves a problem, in particular when high retrieving speed is desired.
In order to increase the retrieving speed it is required to speed up the feed of film. However, with increasing the film-feeding speed it is more difficult to stop the film exactly at the aimed address owing to the inertia of the film-feeding device and the like.
As a solution to the problem it has already been proposed to change the film-feeding speed from high to low before the content of the mark counter reaches the aimed address. But, retrieving according to the solution has been found to often fail to stop that film just at the aimed address. The failure is caused mainly by such that when the film-feeding device is changed over to the lower speed, the film moves in the opposite direction to the feeding direction owing to the inertia of the film reel and other mechanical elements. This phenomenon is well-known to those skilled in the art as back-lash phenomenon. If such a back-lash occurs, then the mark counter counts one mark extra and therefore the coincidence between the number of the counted marks and the address of the desired image is lost. This leads to an error in retrieving data.
According to another prior art retrieving method proposed to solve the above-mentioned problem, the film is fed at first at a high speed until the aimed address and then a film stop instruction is issued at the aimed address to stop the film after over running the aimed address some distance. Thereafter, the film is moved back to the aimed address at a speed sufficiently low enough to stop the film just at the aimed address. However, this retrieving method also has suffered from back-lash. Since the film running at a high speed is abruptly stopped, the film oscillates in the film-feed direction owing to the back-lash or other factors at the stop. As a result, the mark counter may count one mark twice or more, which again leads to error in retrieving data like the first-mentioned solution.